The present invention relates to a piezoelectric resonator vibrating in the thickness shear-slide mode, and more particularly, it relates to an improvement in electric characteristics of such a piezoelectric resonator.
FIG. 5 shows a three-terminal ceramic discriminator, which is an example of a conventional piezoelectric resonator vibrating in the thickness shear-slide mode. The ceramic discriminator, which is applied to a phase shifting circuit for an FM demodulator circuit, comprises an elongated rectangular piezoelectric substrate 20. First and second terminal electrodes 21 and 22 are formed on both end portions of a major surface of the substrate 20, while first and second vibrating electrodes 23 and 24 are adjacently formed close to the terminal electrode 21. The first and second vibrating electrodes 23 and 24 are connected with the first and second terminal electrodes 21 and 22 through thin first and second extracting electrodes 25 and 26 respectively. On another major surface of the piezoelectric substrate 20, a third vibrating electrode 27 is formed to be opposite to the first and second vibrating electrodes 23 and 24, while a third terminal electrode 29 is formed on a central portion of the substrate 20 to be connected to the third vibrating electrode 27 through a third extracting electrode 28. Lead terminals (not shown), for example, are soldered to the terminal electrodes 21, 22 and 29.
In the aforementioned piezoelectric resonator, however, the second extracting electrode 26 connecting the second vibrating electrode 24 with the second terminal electrode 22 is opposed to the third terminal electrode 29 in a area S shown by slant lines in FIG. 5. Therefore, an stray capacitance is caused between the second extracting electrode 26 and the third terminal electrode 29, and hence a capacitance between the first and the third terminal electrodes 21 and 29 differs from that between the second and the third terminal electrodes 22 and 29 so as to cause electrical polarity. Therefore, if input and output terminals of this resonator are reversely connected on a printed circuit board, electric characteristics are inevitably varied. Thus, it is necessary to check the terminal direction of the resonator when it is connected on a printed circuit board.